Kinematic and kinetic analyses of professional pitchers with history of core or groin injuries: A propensity-score matched analysis.

Background: Core injuries in professional baseball pitchers have been linked to both diminished performance and time missed during the season injury was sustained. It is currently unclear how a history of a core injury may affect the future pitching performance and mechanics of professional baseball pitchers. Purpose: To compare kinetic and kinematic variables between professional baseball pitchers with prior core/groin injuries and those without prior injury. Study design: Descriptive laboratory study.
Methods: Professional baseball pitchers with a history of core injury pitched 8-12 fastball pitches while evaluated with 3D-motion capture (480 Hz). Inclusion criteria necessitated that the core injury occurred within one to four-years prior to biomechanical evaluation and that the core injury required time off from professional play for a minimum of 2 weeks and maximum of 3 months. These pitchers were 4:1 propensity-scored matched by age, height, weight, and handedness to pitchers with no prior injury history (control). Twenty kinematic and eleven normalized and non-normalized kinetic parameters were compared between groups using appropriate parametric testing. Sub-analysis of pitchers with distinct core muscle and spinal injuries were also analyzed.
Results: The No Prior Injury (NPI) subgroup (n = 76) had significantly less elbow flexion at ball release (31 ± 5° vs. 35 ± 6° respectfully, p = 0.044) compared to the Core Musculature/Soft Tissue subgroup (CM/ST, n = 10), with no significant difference in kinematics for other injury groups (p > 0.05). The General Core/Groin injury group (GCG, n = 19) had significantly greater normalized elbow anterior force (43.9 ± 4.7 vs. 40.0 ± 5.2 %BodyWeight[BW], p = 0.006) and elbow flexion torque (4.3 ± 0.5 vs. 3.8 ± 0.5 %BWxBodyHeight[BH], p = 0.001) than the NPI pitchers. CM/ST had significantly greater normalized elbow anterior force (p = 0.031), elbow flexion torque (p = 0.002), and shoulder adduction torque (p = 0.007) than NPI pitchers.
Conclusion: Professional baseball pitchers with prior core/groin injuries demonstrated increased elbow anterior force and elbow flexion torque compared to pitchers with no prior core injuries. One possible explanation for this finding includes inadequate recruitment and utilization of the lower extremities as a component of the kinetic chain leading to compensation at the level of the throwing arm. Whether these kinetic differences arise as a consequence of injury or present a risk for such warrants additional investigation.